Sulphite pulp digester system



Jan. 9, 1934. A. CHRISTENSEN SUL-PHITE PULP DIGESTER SYSTEM Fil ed June 16,- 1932 s Sheets-Sheet 1 YIIIIIIIIIIIIIIII/ Jan. 9, 1934. A. CHRISTENSEN 1,942,685

' SULPHITE PULP DIGESTER SYSTEM Filed June 16, 1932 3 Sheets-Sheet 2 Jan. 9, 1934.

A. CHRISTENSEN 1,942,685

SULPHITE PULP DIGESTER SYSTEM Filed June 16, 1932 3 Sheets-Sheet 3 a g. N 1 4 'r mw Patented Jan. 9, 1934 PATENT OFFICE SULPHITE PULP DIGESTER SYSTEM Andreas Christensen, Rhinelander, Wis., assignor to Fibre Making Processesylnc Chicago, 111., a corporation of Illinois Application June 16, 1932. Serial No. 617,572

18 Claims.

This invention relates to the production of wood pulp, and has to do with a system for digesting wood and analogous material.

One of the main objects of my invention is to provide, in conjunction with a digester, a system for circulating the acid liquor and passing it through a heater, the parts of the system being so constructed and related as to reduce cost thereof to a minimum. A further object is to provide a system in which deposition of minerals within the tubes of the heater, resulting in clogging thereof, is avoided. Further objects and advantages of my invention will appear from the detail description.

In the drawings:--

Figure 1 is a side view, partly broken away and in section, of a digester system in accordance with my invention;

Figure 2 is a section taken substantially on line 2-2 of Figure 1, on an enlarged scale;

Figure 3 is a section taken substantially on line 3-3 of Figure 2, parts being broken away;

Figure 4 is an elevation of the upper end portion of the digester and associated parts, partly broken away and in section, illustrating, diagrammatically, the regulator and control valve actuated thereby for controlling escape of gases from the digester, viewed from the side opposite 'to that shown in Fig. l.

The system of my invention includes a digester 1 of known type comprising an outer casing or shell 2 and a lining ,3 which is resistant to the acid used in the digester. neck 4 is provided at the top of the digester and is closed by a removable cover or closure memher. 5. A blow-out fitting 6 in the form of an elbow is secured to the bottom of the digester for convenience in blowing the pulp therefrom and in washing the digester. This fitting is provided with two nipples 7 and 8 to which are connected pipes 9 and 10, respectively, pipe 9 being provided with a suitable valve 11 and pipe 10 being provided with a check valve 12 of known type which permits of flow of liquor through pipe 10 to fitting 6 but prevents reverse flow of the liquor in pipe 10. A discharge pipe 13 is connected to the end of fitting 6, this pipe being provided with a suitable valve 14. The construction of the digester is, in general, known in the art and need not be illustrated nor described here in further detail. v

A tubular screen 15 is supported by brackets 16 in the upper end of digester 1. This screen comprises two portions of arcuate shape in plan,

A charging which define a segment of a circle and extend around the interior of the digester for the greater portion of the circumference thereof. These portions of the screen are secured at one end, by flange and bolt means, to the ends of head 17 of a T member 18, the ends of the portions of the screen remote from T member 18 being closed. Stem 19 (Figure 3) of member fits into the upper end of an elbow 20, the lower end of which fits into, and is bolted or otherwise suitably secured to, the inner end of a sleeve 21 extending through the wall of the digester. This sleeve is provided, adjacent its outer end, with a flange 22 which seats upon and is suitably secured to a flange 23 atthe outer end of a fitting 24 similar to a boiler nozzle, which fitting extends about sleeve 21 in concentric relation thereto, this fitting having a base flange 25 which is suitably secured to shell 2 of the digester exteriorly thereof. A take-01f pipe 26 is suitably secured, by means of a flange 27 at the end thereof, to a flange 28 at the outer end of sleeve2l, This provides a simple and highly eflicient outlet connection for withdrawing liquor from the digester.

Stem 19 of T-member 17 slides within the upper portion of elbow 20 so as to be adjustable vertically relative thereto. The elbow is provided, at its upper end, with an outer flange 30 and stem 19 is provided with a similar flange 31. Securing bolts pass through these flanges and through spacers 32 disposed between the flanges for holding member 17 in predetermined vertical adjustment-relative to the elbow. In order that the screen may be adjusted vertically in accordance with adjustment of member 1'7, the brackets 16 are also capable of vertical adjustment. Each bracket comprises ahead 33 and a stem 34 depending from the head and provided with a vertical slot 35. A supporting pin 36 is suitably secured to the wall of the digester shell and is provided, at its inner end, with a reduced stud 37 passing through slot 35. Stem 34 of the bracket is adjustably secured to pin 36 by means of washers 38 and 39 disposed at opposite faces of the stem, and a nut 40 screwing onto the stud 37. Other suitable means for adjustably supporting the bracket may be employed, if desired, though the means illustrated is preferred as being of simple and durable construction. The ad; instability of the brackets 16 cooperates with the vertically adjustable T member 17 to permit of vertical adjustment of the screen 15. This is advantageous as facilitating positioning of the screen to best advantage. Generally, the screen should be disposed as near the upper end of the digester as is practicable.

The take-off pipe 26 is provided with a control valve 45 of known type operated by a rod 46 connected to a hand wheel 47 supported by a standard 48 on the cook floor 49 at the upper end of the digester. The lower end of pipe 26 is connected to the intake of a pump 50 of known type driven by an electric motor 51., The dis charge of pump 50 is connected to a header 52 at the upper end of a heater 53. This heater is of known type and comprises a lower header 54 to which pipe 10 is connected, a casing -55 extending between the headers and enclosing vertical tubes 56 which establish communication between the upper header and the lower header. Casing 53 is provided at its upper end with a steam inlet nipple 5'7 to which is connected a pipe 58 leading to a suitable source of supply of steam or other heating medium. Adjacent its lower end the casing 53 is provided with a discharge nipple 59 to which is connected a pipe 60 for discharging condensate from the casing. The steam admitted to the casing flows around and between the tubes 56 in intimate contact therewith and serves to heat the liquor flowing through these tubes to the desired temperature. The tubes 56 are of proper interior diameter and sufficient in number to avoid objectionable interference with flow of the liquor circulated through the system, the capacity of the pump being such as to force the liquor through the tubes 56 at appreciable velocity. I

The digester is filled with wood chips and with cooking acid, in the usual manner. The acid, which is a bisulphite solution, is usually a bisulphite of calcium or dolomitic lime, and free sulphur dioxide in excess Ca or mmsoowsoz,

the sulphur dioxide (S O2) combining with the water of the solution to form sulphurous acid (H2803). and the sulphurous acid in turn dissolving the calcium or magnesium to form calcium or magnesium bi-sulphite. During the coo ing operation, the acid liquor is withdrawn from the upper portion of the digester and is passed through the heater. and thence, by means of pipe 10 and fitting 6, to the lower portion of the. digester in which the heated liquor flows upwardly to complete the path of circulation, thus heating the contents of the digester. The pressure within the digester and the temperature of the contents thereof may be varied to meet the requirements of the difierent types of pulp to be made, as is known in the art. The variations in pressure and temperature during the cooking operation, and the reasons for such variations, are known by those skilled in the art and need not be set forth here in detail.

The acid liquor attacks most of the more common metals and causes rapid corrosion thereof. It is necessary, therefore, to construct the parts with which this liquor comes into contact of materials which resist attack by the liquor. Nickel-chromium steel alloy presents high resistance to corrosion by sulphurous acid and, for this reason, is commonly used in digester systems in which the acid liquor is circulated through conduits exterior to the digester. This alloy, while highly efllcient for use with the acid liquor referred to, is quite expensive and the use thereof adds materially to the cost of a digester system. Any saving in the amount of this alloy employed in such a system is, therefore, of considerable practical value, since it results in a material saving in the cost of the system. In the system of my invention the liquor enters the tubes 56 at the upper end of the heater 53 and flows from the lower end of the heater directly to the fitting 6. The heater is thus connected in series in the circulating system and the system exterior of the digester is of minimum overalllength, thus reducing to a minimum the amount of nickelchromium alloy necessary and effecting a material saving in the cost of the system as compared to systems in which the heater and associated parts are not disposed and connected in the manner of my invention.

It is known that, when the acid liquor is heated, the free sulphur dioxide, owing to the unstability of the solution, tends to separate from the liquor and if permitted would escape leaving a solution of calcium or magnesium bi-sulphite. The solubility of free SO: in a solution is in direct relation to temperature and pressure maintained, and to guard against the escape of S02, which would upset the equilibrium of solubility and tend to form insoluble mono-sulphites, it is essential in a system of this type that pressure is maintained in all parts of the system. Otherwise insoluble lime salts would tend to collect upon the walls of the heater tubes and in time form a thick layer or coating which would materially reduce the emciency of the heat exchanger and, eventually, would completely stop the tubes. This tendency of the S0: to separate from the liquor upon heating of the latter may be avoided by using strainers and an intake pipe to circulating pump, of sufli-' cient capacity to guard against a drop in pressure, and maintaining the liquor under considerable pressure when it is heated.

. It is particularly pointed out that the pump 50 delivers to the top header 52 of the heater 53 so that the liquor is forced downwardly through -the tubes 56 under considerable pressure, the direction of flow of the liquor through the tubes being contra to the direction in which the liquor in these tubes tends to flow due to the temperature differences of the liquor. upward flow of the liquor is thus utilized to subject the liquor in the tubes to a slight pressure.

additional to the pressure exerted by the pump, with the result that the liquor in the tubes 56 is maintained under sufiiciently high pressure, while being heated, to prevent separation of the sulphur dioxide from the liquor. This pressure,

combined with the flow of the liquor through the tubes 56 under appreciable velocity, effectively prevents deposition of calcium or other minerals within the heater tubes 56 with the result that the efficiency of the heater remains unimpaired and the flow of the liquor through the heater tubes is not interfered with.

It is pointed out that but a single take-off pipe 26 is employed, and the pipe 10, from the lower end of the heater, is connected to the blow-off fitting 6. This is advantageous as necessitating but one opening through the wall of the digester thus eifecting a further saving in cost, since any The tendency to header 69 which may lead to a suitable recovery apparatus known in the art. Branch pipe 68 is provided with a hand operated valve '70 for opening and closing this branch as required. An automatic valve '71 is disposed in pipe and is connected by a tube '72 to a regulator 73 which, in turn, is connected by a tube '74 to a pressure plug 75 suitably secured through the wall of digester 1. Preferably, I provide a Locke regulator and valve, which are known in the art, and need not be illustrated nor described in detail, it being suflicient to note that I employ a regulator responsive to pressure within the digester, this regulator having operative connection to valve '71 for opening and closing the latter in accordance with variations in pressure within the digester. The regulator 73 is set to open the valve 71 at a predetermined maximum pressure within the digester, and to close the valve when the pressure within the digester is below this predetermined maximum. When valve 71 is opened, valve 6'7 also being opened, the sulphur dioxide gas which has collected in the upper portion of the digester escapes through pipe 65, branch pipe 68 and header 69, from the latter of which it may be conducted to a suitable recovery apparatus above referred to. This provides an automatic control for maintaining the desired pressure within the digester 1, while permitting escape therefrom of the sulphur dioxide when this predetermined pressure is exceeded. This automatic control is particularly efiective when employed with my digester system in which the liquor is heated by being circulated through a heater exterior of the digester.

When cooking wood which is unusually dry, more of the acid liquor is absorbed by the chips than is ordinarily the case with the result that the level of the liquor may be lowered sufiiciently to leave the chips at the top of the digester uncovered, as in Figure 4. These chips, if permitted to become dry, are apt to char and turn black, which is highly objectionable. To avoid this, I preferably provide a return pipe '76, having upper and lower control valves-'7'7 and '78, respectively, and connected at its lower end to upper header 52 of the heater and, at its upper end, to pipe 65 between valves 6'7 and '71. With valves 6'7, '7'7 and '78 open, and valve '71 closed, acid liquor is delivered from pump 50 to header 52 and thence, through pipes '76 and 65 and connection 66, to a. strainer '79 within the digester at the top thereof. This strainer serves to direct the acid liquor in a spray and downwardly onto the exposed chips so as to maintain the latter in a. moist condition and eliminate possibility of charring thereof. Conveniently pipe '76 is connected to pipe 65, as shown, though I contemplate the use of a return pipe entirely separate from pipe 65, when desired or necessary. Pipe '76 may be used at all times, or only when cooking unusually dry wood, as desired. When pipe '76 is not used, valves '77 and '78 are closed, and the system is operated in the manner previouslydescribed. The pump 50 is of adequate capacity to supply the liquor to pipe '76, when used, in ample quantity to keep any exposed chips moist while also forcing the liquor through the heater tubes at suflicient velocity to eliminate any possibility of coating of the tubes with lime salts.

Preferably, the screen 15 comprises a plurality of sections detachably secured together by bolt and flange means at the ends of the respective sections. The head of each bracket includes an arcuate strap member 33a bolted or otherwise removably securedin position and defining, with the main portion of the head, a space conforming in shape to and loosely receiving the flanged ends of the screen sections. port the screen for vertical adjustment, while holding it against relative vertical movement, and also permit of independent expansion and contraction of the screen bothcircurnferentlally and radially thereof.

What I claim is:--

1. In means for digesting wood or the like, a digester, a pump, and a vertical heater having an outlet at its lower end, the intake of the pump being connected to the upper portion of the digester for withdrawing liquor therefrom and the discharge of the pump being connected to the upper end of the heater for delivering thereto the withdrawn liquor under pressure and forcing said liquor downwardly through the heater, the outlet at the lower end of the heater being connected to the lower portion of the digester for delivering thereto the heated liquor.

2. In means for digesting wood L r the like, a digester, a vertical heater, a pump between the top of the digester and the top of the heater, said pump having its intake connected to the digester and its discharge connected to the top of the heater for withdrawing liquor from the digester and delivering it under pressure to the heater at the upper end thereof, and means for delivering the heated liquor from the lower end of the heater to the digester.

3. In means for digesting wood or the like, a. digester, avertical heater, a pump between the top of the digester and'the top of the heater, said pump having its intake connected to the digester adjacent the top thereof and its discharge con nected to the top of the heater for withdrawing liquor from the digester adjacent the top thereof and delivering it under pressure to the heater at the upper end thereof, and means for delivering the heated liquor from the lower end of the heater to-the digester at the lower end hereof.

4. In means for digesting wood or the like, a digester for containing the wood and an acid liquor, a heater, and means for circulating the liquor through the digester and through the heater under positive pressure in a direction contra to the direction which the liquor tends to flow through the heater due to temperature differences in the liquor passing through the heater'.

5. In means for digesting wood or the like, a digester for containingwood and an acid liquor, a pump, a vertical heater, and a blow-out fitting at the bottom of the digester, the intake of the pump being connected to the upper portion of the the digester below the liquor lever therein for withdrawing liquor therefrom and the discharge of the pump being connected to the upper end of the heater for delivering thereto the withdrawn liquor under pressure, the lower end of the heater being connected to said fitting for delivering the heated liquor thereto and thence to the digester.

6. In means for digesting wood or the like, a digester for containing wood and an acid liquor, a vertical heater comprising upper and lower headers and vertical tubes connecting said headers, the lower header having an outlet, said heater also comprising a casing extending between the headers and enclosing said tubes, said casing having means for admission thereto of a heating medium, a pump delivering to the upper header, a conduit connecting the intake of the pump to the upper portion of the digester below the The brackets thus sup-v liquor level therein, and a conduit connecting the outlet of the lower header directly to the lower end of the digester.

7. In means for digesting wood or the like, a digester, a blow-out fitting at the bottom of the digester, and circulating means for withdrawing liquor from the digester and for heating the withdrawn liquor and delivering it to said fitting and thence to the digester.

8. In combination, a digester, a screen within the digester, asleeve extending through the wall of the digester, an elbow extending upwardly within the digester and secured at its lower end to the inner end of the sleeve, and an outlet member leading from the screen and telescoping the upper end of the elbow.

9. In combination, a digester, a conduit extending through the wall of the digester, an elbow extending upwardly within the digester and secured at its lower end to the inner end of the conduit, an outlet T member having its stem telescoping the upper end of the'elbow, means for adjusting said member vertically and for securing it to the elbow, and a screen within the digester and attached to the ends of the head of th T member.

10. In combination, a digester, a conduit extending through the wall of the digester, an elbow extending upwardly within the digester and secured at its lower end to the inner end of the conduit, an outlet T member telescoping the upperend of the elbow, and a screen comprising two portions defining approximately a segment of a circle and extending about the interior of the digester, the respective portions of the screen being secured to the ends of the head of the T member and closed at their ends remote from said member.

11. In combination, a digester, a conduit'extending through the wall of the digester, an elbow extending upwardly within the digester and secured at its lower end to the inner end of the conduit, an outlet T member telescoping the upper end of the elbow, a screen extending about the interior of th digester and attached to the ends of the head of the T member, and brackets attached to the wall of the digester for vertical adjustment and supporting the screen.

12. In combination, a digester, a fitting secured to the wall of the digester exterior thereof and provided at its outer end with an outwardly extending radial flange, a sleeve extending through the wall of the digester and through said fitting, the sleeve having a flange seating on and secured to the flange of the fitting, means including a screen establishing communication between the sleeve and the interior of the digester, and a take-off pipe connected to the outer end of the sleeve.

13. In combination with a digester, a screen within the digester, and means for confining the screen against vertical movement while accommodating independent expansion and contraction of the screen both radially and circumferentially thereof.

14. In means for digesting wood or the like, a digester, a vertical heater; a pump delivering to the upper end of the heater, means connecting the intake of the pump to the upper portion of the digester for withdrawing liquor therefrom, means connecting the lower end of the heater to the lower end of the digester for delivering heated liquor thereto, and a return pipe connected to the upper end of the heater and delivering liquor therefrom into the digester at the top thereof.

15. In means for digesting wood or the like, a

digester, a heater, means connecting the outlet of the heater to the lower portion of the digester for delivering heated liquor thereto, a pump delivering to the inlet of the heater, means connecting the intake of the pump to the upper portion of the digester for withdrawing liquor therefrom, and a return pipe connected to the discharge of the pump and delivering liquor received therefrom under pressure into the digester at the top thereof.

16. In means for digesting wood or the like, a digester, a circulating system comprising a pump and a heater connected in series and to the digester for withdrawing liquor therefrom and passing it through the heater and delivering the heated liquor to the digester, and a return pipe connected to the discharge of the pump and delivering liquor received therefrom.under pressure into the digester at the top thereof.

1'7. In means for digesting wood or the like, a digester, a circulating system comprising a pump and a heater connected to the digester for withdrawing liquor therefrom and passing it through the heater and delivering the heated liquor under pressure to the digester, and a return pipe connected to the digester and to the circulating system for receiving liquor from the latter under pressure and delivering liquor into the digester at the top thereof.

18. In means for digesting wood or the like, a dgester, a circulating system comprising a heater and pressure creating means associated therewith connected to the digester for withdrawing liquor therefrom and passing it through the heater and delivering the heated liquor under pressure to the digester, and a return pipe connected to the digester and to the circulating system for receiving liquor from the latter under pressure and delivering liquor into the digester at the top thereof.

ANDREAS CHRISTENSEN. 

